Publicis started talks to buy the Paris-based agency three months ago and the negotiations could be concluded in coming days, Les Echos said in its report, without describing where it got its information. Spokeswomen from Publicis and Criteo declined to comment.

Publicis CEO Maurice Levy has said that his company is planning smaller acquisitions after it abandoned a $35 billion merger with New York-based Omnicom Group this year. Criteo had an enterprise value of 1.2 billion euros ($1.6 billion) at the end of last year, according to data compiled by Bloomberg.

Advertising agencies including Publicis and WPP, the world's largest, are looking to the digital segment to fuel growth, as revenue in some European and even emerging countries fell short of expectations amid weakened economies. Publicis's digital operations accounted for 41% of its sales in the first half of 2014, up from 37% a year earlier.

Criteo, started in 2005, tracks user activity on websites to help advertisers target potential customers. The software is designed to spot hesitant shoppers online and send them tailored banner ads. Criteo reported revenue of 444 million euros last year, up 63% from a year earlier.